Antenna-based communication systems may utilize beamforming in order to create steered antenna beams with an antenna array or antenna arrays. Beamforming systems may adjust the delay and/or gain of each of the signals transmitted by (or received with in the receive direction) the elements of an antenna array in order to create patterns of constructive and destructive inference at certain angular directions. Through precise selection of the delays and gains of each antenna element, a beamforming architecture may control the resulting interference pattern in order to realize a steerable “main lobe” that provides high beamgain in a particular direction.
Beamforming architectures may conventionally employ one or both of digital and analog radio frequency (RF) processing in order to apply the desired delay and gain factors at each element of the array. Phased antenna arrays are a particularly favored RF beamforming technique for narrowband signals which relies on the approximate equivalence between phase shifts and time delays for narrowband signals. Accordingly, phased antenna arrays may place an RF phase shifter in the signal path of each antenna element and allow the individual phase shift values to be adjusted in order to steer the resulting antenna beam. Although many phased array designs achieve sufficient performance with phase-only control, variable gain amplifiers and other techniques such as tapering may additionally be implemented in order to also allow for gain adjustment.
In contrast to the analog RF processing of RF beamformers, digital beamformers may employ digital processing in the baseband domain in order to impart the desired phase/delay and gain factors on the antenna array. Accordingly, in digital beamforming systems, the phase and gain for each antenna element may be applied digitally to each respective antenna signal in the baseband domain as a complex weight. The resulting weighted signals may then each be applied to a separate radio frequency (RF) chain, which may each mix the received weighted signals to radio frequencies and provide the modulated signals to a respective antenna element of the antenna array. As each antenna element in a digital beamforming system uses an exclusive RF chain, many digital beamforming solutions may use a substantial amount of hardware and thus have considerable cost and power-consumption rates.
Hybrid beamforming solutions may apply beamforming in both the baseband and RF domains, and may utilize a reduced number of RF chains connected to a number of low-complexity analog RF phase shifters. Each analog RF phase shifter may feed into a respective antenna element of the array, thus creating groups of antenna elements that each correspond to a unique RF phase shifter and collectively correspond to a common RF chain. Such hybrid systems may thus reduce the number of RF chains by accepting slight performance degradations resulting from the reliance on RF phase shifters instead of digital complex weighting elements.
In particular for next generation (5G and beyond) cellular systems, Massive MIMO and mm-Wave communications are expected to enable 1000× more data traffic than current cellular systems. Fully digital receiver architectures at a user equipment (UE) may achieve low latency sector sweeping as well as high throughput performance in mm-Wave systems. However, in a fully digital architecture data interfaces (IO links) from analog-to-digital converter (ADC) output (RFIC) to digital baseband processor have high power requirements because a large number of antennas, wide bandwidth, and high throughput mm-Wave RF front-end often uses high-bandwidth and rate interfaces to deliver data to baseband peripherals such as processor and memory. Therefore, approaches that may reduce power consumption may in particular contribute to an implementation of fully digital receiver architectures in practical cellular systems. As power consumption is a general issue, such approaches may further also facilitate implementation of analog, fully connected hybrid, subarray type hybrid, fully digital beamforming architectures, regardless mm-Wave and below 6 GHz systems.
Reducing power consumption may be achieved by reducing the number of 10 links which may rely on spatial compression of ADC output signals. Thereby, spatial compression assuming single-cell (or isolated) environments can already provide efficient compression methods. However, at the digital baseband input a desired signal is often superimposed with intra-cell/inter-cell interference and sometimes even out-of-band blockers which limits effectiveness of such spatial compression approaches.